Jetpack Compose collectAsState 问题

Question

I'm using Composes collectAsState() function to collect from this StateFlow

val _authToken = MutableStateFlow(AuthToken("", 0))
val authToken: StateFlow<AuthToken> = _authToken
val authToken by loginViewModel.authToken.collectAsState() // this returns AuthToken which is fine.

However, when turning a cold flow into a stateflow using the stateIn operator then using collectAsState() it returns a State version of the object which is odd then I need to call.value on collectAsState() to retrieve it.

Does anyone know why this happens?

val user = repository.getUser(viewModelScope).stateIn(viewModelScope, SharingStarted.WhileSubscribed(5000), null)
val user = profileViewModel.user.collectAsState() // returns State<User>

Answer 1

Replace

val user = profileViewModel.user.collectAsState() 

With

val user by profileViewModel.user.collectAsState() 

Answer 2

Well it IS supposed to return State. Compose offers the delegate syntax to allow you to treat state as raw types.

If you want to extract the data from State , you make use of the by keyword. For example,

var a : T by b : State<T> and, var a : State<T> = b : State<T>

In your case, if you want user to be of type User and not State<User> , you should change the initialisation to

val user by profileViewModel.user.collectAsState() // returns User

Also, you should have known from the name of the method, it is collectAs State .

Answer 3

With the new version for androidx.lifecycle:lifecycle-*:2.6.0-alpha01 , use collectAsStateWithLifecycle() instead